1. Field of the Invention
The present invention relates to an apparatus for measuring a magnetic field closely above an integrated circuit or a large-scale-integration device (hereinafter referred to as IC/LSI), an IC/LSI package, and a printed circuit board.
2. Description of the Related Art
FIG. 1A is a schematic view showing an example of a conventional magnetic field measuring apparatus using optical technology. This magnetic field measuring apparatus includes a magneto-optical crystal (hereinafter referred to as MO crystal) as a magnetic field detecting element, optical fibers, and optical devices. Such a magnetic field measuring apparatus is disclosed in, for example, Tsuchiya, Yamazaki, Wakana, and Kishi, “Hikari faiba tan jiki kogaku (FEMO) purobu ni yoru bisho ryoiki maikuro ha tai jikai bumpu sokutei (Microscopic Distribution Measurements of Microwave Frequency Magnetic Fields by Fiber-Edge Magneto-Optic (FEMO) Probing)”, Nihon Oyo Jiki Gakkaishi (Journal of the Magnetics Society of Japan), Vol. 26, No. 3, pp. 128-134 (2002) (hereinafter referred to as Document 1).
FIG. 1B is an enlarged view of the end portion of this magnetic field measuring apparatus. The end portion includes an optical fiber 3, an MO crystal 12 attached to the end of the optical fiber 3, and a dielectric film 13 formed onto the bottom of the MO crystal 12. The dielectric film 13 is for reflecting light incident on the MO crystal 12.
The principle of magnetic field detection in this magnetic field measuring apparatus will be described schematically below. The light emitted from a continuous-wave-generating semiconductor laser light source 2 is amplified by a fiber amplifier (light amplifier) 4-1. The amplified light passes through a polarization controller 5 and an optical circulator 6, and becomes perpendicularly incident on the MO crystal 12 from the end of the optical fiber 3. The incident light is reflected by the dielectric film 13 formed onto the bottom of the MO crystal 12, and returns to the optical fiber 3. Between incidence on the MO crystal 12 and return to the optical fiber 3, the light is polarization-modulated due to the Faraday effect according to the intensity of an external magnetic field.
The polarization-modulated light passes through the optical circulator 6 again, and is then intensity-modulated by an analyzer 7. The intensity-modulated light is amplified by another fiber amplifier 4-2 and then converted photoelectrically by a photodetector 8. The photocurrent from the photodetector 8 is input into a spectrum analyzer 10 through a coaxial cable 9. The spectrum analyzer 10 detects the peak of the photocurrent as a signal caused by the external magnetic field.
In the principle of this measuring system, since the intensity of the signal detected by the spectrum analyzer 10 varies according to the intensity of the external magnetic field, the magnetic field distribution can be measured by changing the position of the MO crystal 12 above a measured object 11.
When the external magnetic field is measured by using the conventional magnetic field measuring apparatus shown in FIGS. 1A and 1B, the spatial resolution is determined by the volume of the probe light propagating in the MO crystal 12. The smaller the volume of the probe light, the higher the spatial resolution.
As shown in FIG. 2, the volume of a probe light 15 in the MO crystal 12 is approximately defined as the volume of the following cylinder. That is to say, the volume of the probe light in the crystal is equal to the volume of the cylinder having a diameter equal to the diameter of a core 14 of the optical fiber 3 and a height equal to the thickness of the MO crystal 12. This is disclosed in, for example, Wakana, Yamazaki, Iwanami, Hoshino, Kishi, and Tsuchiya, “Study of the Crystal Size Effect on Spatial Resolution in Three-Dimensional Measurement of Fine Electromagnetic Field Distribution by Optical Probing”, Jpn. J. Appl. Phys. Vol. 42 (2003), pp. 6637-6640 (hereinafter referred to as Document 2).
The hitherto known magnetic field measuring apparatus has an end portion including an optical fiber with core diameter about 10 μm and an MO crystal with thickness 11 μm. It is reported that this magnetic field measuring apparatus has a spatial resolution capable of distinguishing the magnetic field generated from parallel conductors spaced at a distance of 10 μm and constituting a zigzag wiring. This is disclosed in, for example, Iwanami, Hoshino, Kishi, and Tsuchiya, “Magnetic Near-Field Distribution Measurements over Fine Meander Circuit Patterns by Fiber-Optic Magneto-Optic Probe”, Proc. 2003 IEEE Symp. on Electromagnetic Compatibility, pp. 347-352, Aug. 18-22 (2003) (hereinafter referred to as Document 3). That is to say, the conventional magnetic field measuring apparatus using optical technology has achieved a 10-μm-level spatial resolution.
As described above, a magnetic field measuring apparatus having a 10-μm-level spatial resolution has been achieved. However, the 10-μm-level spatial resolution is inadequate for searching the source of electromagnetic interference (hereinafter referred to as EMI) in electronic devices or electronic circuits. An IC/LSI is a typical object searched for EMI sources. When a recent LSI chip or a compact LSI package having microscopic wiring is measured, a magnetic field measuring apparatus with higher spatial resolution is desired.
As described above, in the case of the magnetic field measuring apparatus including an MO crystal and optical devices, the spatial resolution is determined by the volume of the probe light propagating in the MO crystal. Therefore, in order to achieve a magnetic field measuring apparatus with a spatial resolution higher than that of the conventional magnetic field measuring apparatus including an MO crystal and optical devices, it is necessary to reduce the volume of the probe light in the MO crystal.